Rotation support apparatus for compressor pulley

ABSTRACT

A radial ball bearing  14  of the three point contact type or four point contact type is used for the rolling bearing for a compressor pulley. The offset amount δ, that is the axial distance between the center α of the radial load applied to the follower pulley  4  from the endless belt  11,  and the center β of the radial ball bearing  14  is 40% or less of the diameter of the pitch circle. In addition, the radial clearance of the radial ball bearing  14  is 0.2% or less of the diameter of the pitch circle. With this construction, the durability of the rolling bearing to support the follower pulley  4  is secured while made compact.

FIELD OF THE INVENTION

[0001] This invention relates to a rotation support apparatus for acompressor pulley, and more particularly to a compressor pulley supportapparatus which is installed for use in the rotation drive apparatus ofa compressor for the air-conditioning apparatus of an automobile so asto support a follower pulley at the stationary portion, such as thehousing, of the compressor such that the follower pulley can rotatefreely for rotation drive of the compressor.

DESCRIPTION OF THE RELATED ART

[0002] The compressor installed in the air-conditioning apparatus of anautomobile for compressing refrigerant is rotated by the engine forautomobile operation. Therefore, there is an endless belt that runsbetween the follower pulley that is formed on the end of the rotatingshaft of the compressor and the drive pulley that is fastened to the endof the crankshaft of the engine, and the rotating shaft of thecompressor is rotated by the rotation of this endless belt.

[0003]FIG. 7 shows a construction of the rotation drive section of therotating shaft 1 of the compressor. This rotating shaft 1 is supportedinside a casing 2 by a rolling bearing (not shown in the figure) suchthat it rotates freely. A follower pulley 4 is rotatably supportedaround the support cylinder section 3 that is formed on the outersurface on the end of the casing 2, by a multi-row radial ball bearing5. This follower pulley 4 is entirely ring shaped with a U-shaped crosssection, and a solenoid 6 that is fastened to the end surface of thecasing 2 is located in the space inside the follower pulley 4.

[0004] On the other hand, there is an installation bracket 7 that isfastened on the end of the rotating shaft 1 in the section thatprotrudes from the casing 2, and a ring-shaped plate 8 that is made of amagnetic material is supported by way of a plate spring 9 around thisinstallation bracket 7. This ring-shaped plate 8 is separated from thefollower pulley 4 as shown in FIG. 7 by the elastic force of the platespring 9 when there is no electric current flowing to the solenoid 6,and it is attracted toward the follower pulley 4 when there is electriccurrent flowing to the solenoid 6, such that rotation force is freelytransmitted to the rotating shaft 1 from the follower pulley 4. In otherwords, the solenoid 6, ring-shaped plate 8 and plate spring 9 form anelectromagnetic clutch 10 for engaging and disengaging the followerpulley 4 and rotating shaft 1.

[0005] As described above, when the follower pulley 4 is supported by adouble-row radial ball bearing 5 such that it rotates freely, and whenan eccentric load is slightly applied to the follower pulley 4 from theendless belt 11 that extends around the follower pulley 4, rarely doesthe center axis of the outer race 12 of the double-row radial ballbearing 5 come out of alignment (become tilted) with the center axis ofthe inner race 13. Moreover, this construction makes it possible tosufficiently secure the durability of the double-row radial ball bearing5, as well as prevent tilting of the rotation axis of the followerpulley 4 and eccentric wear of the endless belt 11.

[0006] However, by using the double-row radial ball bearing 5, it isimpossible to avoid an increase in dimensions in the axial direction. Inmany cases, the rotation support section for the follower pulley 4 mustbe located in a limited space, and therefore any increase in dimensionsin the axial direction is not preferable. In addition, as the dimensionsin the axial direction increase, the cost of component parts alsoincreases.

[0007] In the case that a single-row, deep-groove radial ball bearing isused instead of the double-row radial ball bearing 5 as the rollerbearing for supporting the follower pulley 4, it becomes easier toreduce the dimensions in the axial direction and to fit the bearing in alimited space. However, in the case of a single-row, deep-groove radialball bearing, when the follower pulley 4 receives a moment load, theforce for preventing tilting of the follower pulley 4 is small so themisalignment of the center axis of the outer race of the radial ballbearing with the center axis of the inner race becomes severe. As aresult, durability of the radial ball bearing becomes inadequate and itbecomes easy for excessive eccentric wear of the endless belt 11 thatextends around the follower pulley 4 to occur.

[0008] In consideration of the aforementioned problems, use of asingle-row, 4-point contact radial ball bearing for supporting thefollower pulley, as disclosed in Japanese Patent Publications Nos.Tokukai Hei 9-119510, and Tokukai Hei 11-336795, has been known. FIG. 8and FIG. 9 show a second example of the prior construction as disclosedin Japanese Patent Publication No. Tokukai Hei 9-119510.

[0009] In this second example of the prior construction, the followerpulley 4 is made of sheet metal by a bending process such as pressing,and is such that it can be rotatably supported around a support section(not shown in the figure) by a single-row, 4-point contact radial ballbearing 14. This radial ball bearing 14 comprises an outer race 15 andinner race 16, which are concentrically supported, and a plurality ofballs 17. Of these, an outer-ring raceway 18 is formed around the innerperipheral surface of the outer race 15, and an inner-ring raceway 19 isformed around the outer peripheral surface of the inner race 16. Both ofthese raceways 18, 19 have a gothic arch-shaped cross section having apair of arcs that both have a radius of curvature that is more than ½ ofthe diameter of the balls 17 and intersect each other at the midportion. Accordingly, the rolling surface of the balls 17 comes intocontact with the raceways 18, 19 at two points respectively, so thatthere are four contact points in total for each of the balls 17.

[0010] This kind of 4-point contact type radial ball bearing 14 is morerigid against moment loads than a typical single-row, deep-groove radialbearing, and when a moment load is received, it is very difficult forthe center axis of the outer race 15 to come out of alignment with thecenter axis of the inner race 16. Therefore, it is possible to alleviateeccentric wear to the endless belt 11 (see FIG. 7) that extends aroundthe follower pulley 4 when compared with a pulley rotation supportapparatus for a compressor that uses a typical single-row, deep-grooveradial ball bearing.

[0011] In Japanese Patent Publication No. Tokukai Hei 11-336795, the4-point contact type radial ball bearing described above is assembled inthe rotation support section of the follower pulley for the compressordrive, and furthermore, an electromagnetic clutch is placed between thefollower pulley and the rotating shaft of the compressor.

[0012] Moreover, as shown in FIG. 10, even in the case of a single-rowball bearing 14 of the 3-point contact type, the rigidity against momentloads is greater than for a typical single-row, deep-groove radial ballbearing, and when a moment load is received, it is difficult for thecenter axis of the outer race 15 to come out of alignment with thecenter axis of the inner race 16. This 3-point contact type ball bearing14 has an inner-ring raceway 19 formed around the outer peripheralsurface of the inner race 16 such that its cross section is arc shapedto have a single radius of curvature that comes in contact with therolling surface of the ball 17 at one point, and a gothic arch-shapedouter-ring raceway 18 formed around the inner peripheral surface of theouter race 15, that comes in contact at two points with the rollingsurface of the ball 17 in the same way as the radial ball bearing 14 ofthe 4-point contact type shown in FIG. 9. In the case of supporting thepulley of a compressor with this kind of 3-point contact ball bearing 14as well, it is possible to alleviate eccentric wear to the endless belt11 (see FIG. 7) that extends around the follower pulley 4 when comparedwith a pulley rotation support apparatus for a compressor that uses atypical single-row, deep-groove radial ball bearing.

[0013] In contrast to the construction shown in FIG. 10, a 3-pointcontact type ball bearing in which the rolling surface of the ball comesin contact with the outer-ring raceway at one point, and the inner-ringraceway at two points, has the same effect.

[0014] As mentioned above, in the case of assembling a 3-point contactradial ball bearing or 4-point contact radial ball bearing in thesupport section for rotatably supporting a follower pulley for thecompressor drive, it is possible to sufficiently secure both of thecompact size, lightness of weight and the durability of the bearing.However, in these prior art cases, since the dimensions of all partswere not sufficiently examined, it was not always possible to obtainadequate results.

SUMMARY OF THE INVENTION

[0015] An objective of this invention is to provide a rotation supportapparatus for compressor pulley that will solve the problems describedabove.

BRIEF DESCRIPTION OF THE INVENTION

[0016]FIG. 1 is a cross sectional view of a portion of one example ofthe embodiment of the present invention.

[0017]FIG. 2 is an enlarged cross sectional view of the radial ballbearing taken out of the example of FIG. 1.

[0018]FIG. 3 is a cross sectional view of a portion of the raceway witha ball thereon to explain the concept of the groove depth.

[0019]FIG. 4 is a diagram to show a relation between the effectiveradial clearance and the height of the contact ellips.

[0020]FIG. 5 is a diagram to show a relation between the displacementamount of ball from the normal position and the circumferentialposition.

[0021]FIG. 6 is a diagram to show a result of durability tests which isconducted to know about the effects of the ratio of the offset amount tothe diameter of the pitch circle on the durability.

[0022]FIG. 7 is a partial cross sectional view to show a first exampleof the conventional structure.

[0023]FIG. 8 is a partial cross sectional view to show a second exampleof the conventional structure.

[0024]FIG. 9 is a partial enlarged view to show the radial ball bearingof the four point contact type.

[0025]FIG. 10 is a partial enlarged view to show the radial ball bearingof the three point contact type.

[0026]FIG. 11 is a cross sectional view to show another example of theconstruction to which the present invention is applied.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0027] The rotation support apparatus for compressor pulley of thisinvention comprises: in the same way as that of the conventionalcompressor pulley support apparatus described above, a rotating shaft; astationary support section that is formed around the rotating shaft; arolling bearing that is supported by this stationary support section;and a pulley that is supported by the rolling bearing such that itrotates freely around the support section, and around which an endlessbelt is extended.

[0028] Moreover, similar to the rolling bearing disclosed in JapanesePatent Publications Nos. Tokukai Hei 9-119510 and Tokukai Hei 11-336795described above, the rolling bearing is a radial ball bearing of thesingle-row 3-point contact type or 4-point contact type, whichcomprises: an inner race having an inner-ring raceways formed around itsouter peripheral surface that is shaped such that it comes in contactwith the rolling surface of the balls at one or two points; an outerrace having an outer-ring raceway formed around its inner peripheralsurface that is shaped such that it comes in contact with the rollingsurface of the balls at one or two points; and a plurality of ballslocated and freely rotating between the inner-ring raceway andouter-ring raceway; and where at least one of the inner-ring raceway andouter-ring raceway comes in contact with the rolling surface of each ofthe balls at two points.

[0029] Particularly, in the case of the rotation support apparatus forcompressor pulley of this invention, the offset amount, specificallydistance in the axial direction between the center of the endless beltcoming in contact with the outer peripheral surface portion of thepulley and the center of the radial ball bearing is 40% or less of thediameter of the pitch circle of the radial ball bearing.

[0030] Preferably, the radial clearance for a standalone radial ballbearing (before the inner and outer races are fitted with the matingmembers) is 0.2% or less of the diameter of the pitch circle of theradial ball bearing, or 1.5% or less of the diameter of the balls.

[0031] Moreover, it is preferable that the aforementioned offset amountis 20% or less of the diameter of the pitch circle, and even morepreferable that it is 10% or less. Furthermore, when necessary, thelower limit of the offset amount can be 1 mm or greater.

[0032] Furthermore, it is preferable that the invention is combined withone or two or more of the following items 1 thru 5 in construction.

[0033] 1. The groove depth of the inner-ring raceway and outer-ringraceway is 18% or more of the diameter of the balls.

[0034] 2. The radial ball bearing is filled with grease containing abase oil, which is one or two or more synthetic oils selected from thegroup of ether, ester and poly α olefin oils, a urea thickening agent,and at least Ba, Zn and ZnDTC as additives.

[0035] 3. At least one process of the nitriding and dimensionstabilization is performed for at least one member of the inner race,outer race and balls.

[0036] 4. The balls are held in the pockets of a retainer such that theycan rotate freely, and the inner dimension of the pockets in thecircumferential direction of the retainer is 1.03 times or more than thediameter of the balls.

[0037] 5. The width dimension of the cross-section of the radial ballbearing is 1.3 times or more than the height dimension in the radialdirection.

[0038] The items 1 thru 5 in construction above, separate from thepresent invention, and independently or arbitrarily in combination, canbe applied to the radial ball bearing of the 3-point or 4-point contacttype of the rotation support apparatus for compressor pulley.

[0039] With the rotation support apparatus for compressor pulley of thisinvention, constructed as described above, it is possible to suppressany increase in the rotation resistance of the radial ball bearing,while at the same time suppress misalignment of the center axis of theinner race of the radial ball bearing from the center axis of the outerrace. In other words, the amount of offset of the winding position ofthe endless belt from the center of the radial ball bearing is kept to40% or less of the diameter of the pitch circle of the radial ballbearing, so that it is possible to keep moment loads applied to theouter race by way of the pulley to a minimum.

[0040] This makes it possible to suppress tilting of the pulley andouter race with respect to the inner race, as well as makes it possibleto prevent excessive surface pressure from occurring in the rollingcontact portion of the radial ball bearing, thus making it possible tosecure the durability of the radial ball bearing. In addition, it ispossible to keep eccentric wear of the endless belt that extends aroundthe pulley to a minimum, making it possible to secure the durability ofthe endless belt.

[0041] Moreover, by keeping the radial clearance of the radial ballbearing upon standalone 0.2% or less of the diameter of the pitch circleof the radial ball bearing, or 1.5% or less of the diameter of theballs, it becomes more difficult for the concentric center axes tobecome misaligned, and improved operation is obtained.

[0042] Furthermore, when necessary, by adding one or two or more of theitems 1 thru 5 above, it is possible to further improve the durabilityof the radial ball bearing.

[0043] First, by securing the groove depth of the inner and outerraceways to 18% or more of the diameter of the balls as described initem (1), it is possible to prevent the rolling surface of the ballsfrom moving onto the edge of the inner-ring raceway or outer-ringraceway, and it is possible to prevent excessive surface pressure frombeing applied to the rolling surface, thus making it possible to securethe rolling fatigue life of the rolling surface and improve thedurability of the radial ball bearing.

[0044] Moreover, by filling the bearing with grease having a compositionas specified in item (2) above, it is possible to improve the life ofthe grease, and thus it is possible to improve the durability of theradial ball bearing.

[0045] Also, by performing nitriding or dimension stabilization asdescribed in item (3) above, it is possible to improve the rollingfatigue life of the treated parts, as well as the other parts that comein contact with the treated parts, and thus it is possible to improvethe durability of the radial ball bearing.

[0046] Moreover, by securing the internal dimension of the retainerpockets, it is possible to prevent the balls in the pockets fromstrongly pressing against the inner surface of the pockets, and thus itis possible to prevent damage to the retainer and to improve thedurability of the radial ball bearing, which includes this retainer.

[0047] Furthermore, by securing the width dimension of the cross sectionof the radial ball bearing as described in item (5) above, it ispossible to increase volume of the space inside the radial ball bearingand the amount of grease that can be filled into that space, and as aresult it is possible to lengthen the life of the grease and improve thedurability of the radial ball bearing.

[0048] As can be seen from the explanation above, the construction ofthe items (1) thru (5) above can be applied separately or arbitrarilycombined and applied to the rotation support apparatus for compressorpulley of this invention. Furthermore, these items can be applied to asingle-row ball bearing, regardless of whether it is a radial ballbearing of the 3-point contact type or 4-point contact type,independently (separately) from the rotation support apparatus forcompressor pulley of this invention. In this case as well, theconstruction of items (1) thru (5) above can be applied separately orarbitrarily combined.

[0049] Now, the present invention is explained on the embodimentsreferring to the attached drawing.

[0050]FIG. 1 and FIG. 2 show a first example of the embodiment of theinvention. This embodiment is characterized by construction of using a4-point contact type radial ball bearing 14 as the roller bearing forrotation support of the follower pulley 4 around the stationary supportsection such as the support cylinder 3 of the casing 2, and by properlyregulating the positional relationship between the radial ball bearing14 and follower pulley 4 by the relationship with the dimensions of thisradial ball bearing 14, it is possible to secure the durability of theradial ball bearing 14 and the endless belt 11, which extends around thefollower pulley 4. The construction and function of the other parts aresubstantially the same as in the prior construction shown in FIG. 7 anddescribed above, so the same symbols will be used for like parts, andany redundant explanation will be omitted or simplified, and thisexplanation will center on the characteristic parts of this embodiment.

[0051] The aforementioned radial ball bearing 14 comprises an outer race15 and inner race 16, which are supported such that they are concentricwith each other, and a plurality of balls 17. There is an outer-ringraceway 18 formed around the inner peripheral surface of the outer race15, and an inner-ring raceway 19 formed around the outer peripheralsurface of the inner race 16. The cross section of these ring raceways18, 19 is a gothic arches shape with a pair of two arcs that intersectin the middle of the arcs and which have different centers and radii ofcurvature Ro, Ri that are more than ½ of the diameter Da of the balls17. In this example, the radius of curvature Ro of the outer-ringraceway 18 is 0.53 times the diameter Da of the balls 17 (Ro=0.53 Da),and the radius of curvature Ri of the inner-ring raceway 19 is 0.515times the diameter Da of the balls 17 (Ri=0.515 Da).

[0052] With the construction described above, the ring raceways 18, 19both come in contact with the rolling surface of the ball 17 at twopoints for a total of four contact points for each ball 17. In thisexample, the rest angle θ, which indicates the positions of the rollingcontact sections between the raceways 18, 19 and the rolling surface ofthe ball 17 by way of the displacement angle from the center of theraceways 18, 19, are each 20 degrees.

[0053] Also, when the radial ball bearing 14 is assembled with theaforementioned outer race 15, inner race 16 and balls 17, there ispositive or negative radial clearance in the radial ball bearing 14,however, even when there is positive clearance, that value is kept to0.2% or less of the diameter Dp of the pitch circle of the radial ballbearing 14, or 1.5% or less of the diameter Da of the balls 17.

[0054] The reason that the radius of curvature Ro of the outer-ringraceway 18 is made larger than the radius of curvature Ri of theinner-ring raceway 19 is that the convex-concave shape with respect tothe circumferential direction of the raceways 18, 19 becomes oppositefor the outer-ring raceway 18 and inner-ring raceway 19. In other words,by making the radius of curvature Ro of the outer-ring raceway 18 whichhas a concave shape with respect to the circumferential direction,larger than the radius of curvature Ri of the inner-ring raceway 19which has a convex shape with respect to the circumferential direction,there is no large difference in contact area and contact pressure of thecontact sections and the rolling fatigue lives of the races 18, 19 arematched, so design is simplified.

[0055] Moreover, depending on the operating conditions, high-temperaturetempering in the temperature range of 190° C. to 230° C. or 230° C. to270° C. is performed for the outer race 15 and inner race 16, in orderto improve the rolling fatigue life of the raceways 18, 19. Whenhigh-temperature tempering is actually performed, it is performed withina temperature range at nominal values of 200° C., 210° C., 220° C., 240°C., or 260° C. as targets.

[0056] In the example shown in the figures, in the centers in the widthdirection of the raceways 18, 19, escape grooves 20 a, 20 b are formedin order to prevent interference with the tools used when processing theraceways 18, 19. However, these escape grooves 20 a, 20 b can be omittedas in the case of the prior construction previously described and shownin FIG. 9.

[0057] In any case, the material thickness T₁₅ of the bottom section ofthe groove (part in the center of the outer-ring raceway 18 with thesmallest thickness) in the outer race 15 is 20% or more, and preferably20 to 40% of the diameter Da of the balls 17 {T₁₅=(0.2 to 0.4)Da}. Whenthe escape groove 20 a is formed, the material thickness T₁₅ is thedistance between the bottom section of the escape groove 20 a and theouter peripheral surface of the outer race 15. By regulating thismaterial thickness T₁₅ within the aforementioned range, it is possibleto prevent useless increase in the diameter of the radial ball bearing14, and thus it is possible to prevent increasing the size of the radialball bearing 14, which contains the outer race 15, and secure thestrength of the outer race 15.

[0058] It is also preferable that the groove depth of the inner-ringraceway 19 and outer-ring raceway 18 be 18% or more of the diameter Daof the balls 17. As shown in FIG. 3, the groove depth of the inner-ringraceway 19 and outer-ring raceway 18 of a 4-point contact type radialball bearing is the distance H from the curved bottom section, havingthe aforementioned radius of curvature Ri (Ro), to the edges of theinner-ring raceway 19 and outer-ring raceway 18 (in the case ofchamfered edges, it is the distance to the chamfered section). By makingthis groove depth H 18% or more of the diameter Da of the balls 17, itis possible to prevent the rolling surface of the balls 17 from ridingup on the edges of the inner-ring raceway 19 and outer-ring raceway 18,and prevent large surface pressure from being applied to the rollingsurface, and thus it is possible to secure the rolling fatigue life ofthe rolling surfaces and improve the durability of the radial ballbearing 14. The reason for this will be explained used FIG. 3 and FIG.4.

[0059] There is a pair of well known contact ellipses 33 formed at thecontact sections between the rolling surface of the balls 17 and theinner-ring raceway 19 and outer-ring raceway 18, on the left and right(left and right direction of FIG. 3) of the raceways 18, 19, however,the size of these contact ellipses 33 varies according to the size ofthe radial load or moment load applied to the radial ball bearing 14.When a moment load is applied, the sizes of the pair of contact ellipses33 differ from each other.

[0060] In any case, when the contact ellipses 33 exist entirely in thesection of the inner-ring raceway 19 and outer-ring raceway 18,excessively large surface pressure is not applied to the rolling surfaceof the balls 17, however, when either of the contact ellipses 33 becomeseparated from the inner-ring raceway 18 or outer-ring raceway 19(strictly speaking, when the ellipses becomes separated, they are nolonger contact ellipses, but in order to simplify the explanation, theterm “contact ellipse” will be used here even when the area of contactreaches the edges), very large pressure forces act on the rollingsurfaces due to edge loading.

[0061] Moreover, in order to secure the rolling fatigue life of therolling surface of the balls 17 and the durability of the radial ballbearing 14, it is necessary that the contact ellipses 33 do not becomeseparated from the inner-ring raceway 19 or outer-ring raceway 18, or inother words, it is necessary that the contact ellipses 33 do not reachthe edges of the ring raceways 19, 18.

[0062] Therefore, the inventors performed experiments to find therelationship between the effective radial clearance and height of thecontact ellipses 33 for a 4-point contact type radial ball bearing 14that is being operated under moment loading. The experiments wereperformed using the specifications as described above using FIG. 2,where a 1,000 N radial load was applied to a radial ball bearing 14having a pitch-circle diameter Dp of 43.5 mm, at an offset amount of 8.7mm (in FIG. 1, δ=8.7 mm, δ/D=0.2=20%), and the change in height of thecontact ellipses 33 due to fluctuation of the effective radial clearancewas found.

[0063] The contact ellipses 33 existed at 4 points for each ball 17 ofthe 4-point contact type radial ball bearing 14, however, of these, theheight h of the edge section of the contact ellipse 33 that reachednearest to the edge section of the raceways was taken to be the heightof the contact ellipse 33 of the radial ball bearing 14. Also, therelationship between the ratio (h/Da) of this height h with respect tothe diameter Da of the balls 17, and the effective radial clearance wasfound.

[0064] The results of the experiments are shown in FIG. 4. The 4-pointcontact type radial ball bearing 14 that is assembled in the rotationsupport section of the pulley for compressor to which this invention isdirected is used under temperature conditions of −40° C. to 160° C., andthe effective radial clearance of the radial ball bearing 14 in thiscase is in the range from −0.010 mm (negative clearance) to 0.020 mm(positive clearance). In this range, the height h of the contact ellipse33 is the highest since the effective radial clearance is the greatest,and when the effective radial clearance is 0.020 mm, the ratio (h/Da) ofthe height h of the contact ellipse 33 with respect to the diameter Daof the balls 17 was 18%.

[0065] From this result, it can be seen that as described in item (1)above, when the groove depth H of the inner-ring raceway 19 andouter-ring raceway 18 is secured at 18% or more of the diameter Da ofthe balls 17, it is possible to prevent the rolling surface of the balls17 from riding up on the edges of the inner-ring raceway 19 andouter-ring raceway 18. By preventing the rolling surface from riding upon the edges, it is possible to prevent excessively large surfacepressure from being applied to the rolling surface of the balls 17, andthus making it possible to secure the rolling fatigue life of therolling surface and improve the durability of the radial ball bearing14. Taking into consideration the work of assembling the balls 17 inbetween the inner-ring raceway 19 and outer-ring raceway 18, the maximumvalue of the ratio (H/Da) of the groove depth H with respect to thediameter Da of the balls 17 is taken to be 40% or less.

[0066] This technique of improving the durability of the radial ballbearing 14 by keeping the groove depth H of the inner-ring raceway 19and outer-ring raceway 18 at 18% or more of the diameter Da of the balls17, can of course be combined with this invention, directed to thecompressor pulley rotation support section as well as applied to otheruses.

[0067] Moreover, as shown in FIG. 2, an attachment groove 21 is formedaround the inner peripheral surface on both ends of the outer race 15,in which the outer peripheral edges of seal rings 22 are fastened. Theseseal rings 22 comprise an elastic material 24, which is reinforced by ametal core 23, and the outer peripheral edge of the elastic material 24are fitted elastically inside the aforementioned attachment grooves 21.In this state, the tip of the edge of a seal lip 25 that is formed onthe inner peripheral edge of the elastic material 24 comes in slidingcontact all the way around a section of the inner race 16, and sealsboth openings of the internal space 26 where the balls 17 are located.It is preferable for nitrile rubber or acrylic rubber to be used for theelastic material 24 of the seal rings 22.

[0068] The internal space 26 is sheltered from the outside in this way,and then as described for item (2) above, an ether-family grease (notshown in the figure) having a viscosity of 70 to 90 mm²/s (cst) andpreferably 77 to 82 mm²/s, is filled in the space at a temperature of40° C. It is preferable for this grease to be a synthetic oil havingether-family oil as the base oil, and to contain a urea thickening agentsuch as diurea, and at least Ba, Zn and ZnDTC. (extreme-pressureadditive Zinc Dithiocarbamate) as additives. This kind of grease formsan oil film on the rolling contact surfaces of the balls 17 and raceways18, 19, which contributes to securing of the rolling fatigue life of theraceways 18, 19. In other words, when the inside of the radial ballbearing 14 becomes hot due to operation under conditions of a largeoffset load, the life of the grease filled in the internal space 26 isshortened due to thermal degradation. Grease having the compositiondescribed above has superior thermal resistance, so the life of thegrease drop very little due to rise in temperature inside the internalspace 26, which contributes to the improvement of durability of theradial ball bearing 14. In addition to grease having the compositiondescribed above, it is also possible to fill the internal space 26 witha grease having an ester-family or poly α olefin-family synthetic oil asthe base oil.

[0069] In this example of the invention, the balls 17 are held by acrown-shaped retainer or cage 27 such that they can rotate freely. Thisretainer 27 is formed into a single piece by injection molding of asynthetic resin such as polyamide resin or polyphenylene sulfide resinwhich contains 5 to 35% by weight (preferably 10 to 25% by weight) glassfiber as a reinforcement material. The thickness T₂₈ in the axialdirection of the bottom section of this retainer 27, or in other words,the portion of the circular rim section 28 that is the thinnest andwhich corresponds to the innermost portion of the pockets 29, is 10 to40% of the diameter Da of the rolling balls 17 {T₂₈=(0.1 to 0.4) Da}. Byregulating the dimensions of the retainer 27 as described above, it ispossible to keep any increase in the dimensions in the radial directionof the retainer 27 to a minimum, while at the same time securing thestrength of the retainer 27, and regardless of centrifugal force that isapplied when the follower pulley 4 is rotating at high speed, it ispossible to keep elastic deformation of this retainer 27 within anamount that causes no practical problems.

[0070] Moreover, it is preferable that the internal dimension of thepockets 29 in the circumferential direction (front and rear in FIGS. 1and 2) of the retainer 27 be 1.03 times or more the diameter Da of theballs 17. By securing the internal dimension of the pockets 29 of theretainer 27 in this way, it is possible to prevent strong pressingforces from acting on the inner surface of the pockets 29 by balls 17that are held inside the pockets 29, and this it is possible to preventdamage to the retainer 27 and to improve the durability of the radialball bearing 14 that includes this retainer 27. The reason for this willbe explained using FIG. 5.

[0071] The aforementioned retainer 27 rotates as the balls 17 revolve,however, the revolution speed of the balls 17 are affected by thecontact angle with the outer-ring raceway 18 and inner-ring raceway 19.Also, when the radial ball bearing 14 rotates in a state of momentloading, the contact angle with the balls 17 changes a little in thecircumferential direction of the outer-ring raceway 18 and inner-ringraceway 19.

[0072] As a result, the revolution speed of the balls 17 becomesnon-uniform in this circumferential direction. In other words, the speedslightly increases or decreases depending on the phase in thecircumferential direction. As a result, the position of the balls 17 inthe circumferential direction slightly changes with reference to thenormal position in the case where the revolution of the balls 17 wasuniform (no change in revolution speed in the circumferentialdirection).

[0073]FIG. 5 shows the ratio of the displacement of the balls 17 fromthe normal position with respect to the diameter Da of the balls 17 whenthe radial ball bearing 14 a is rotating under moment loading. Theabscissa in FIG. 5 represents the position in the circumferentialdirection by the angle, and the ordinate represents the ratio of thedisplacement from the normal position with respect to the diameter Da ofthe balls.

[0074] As can be clearly seen from FIG. 5, while the balls 17 arerevolving one rotation, they move forward or backward about ±1.7% in thedirection of rotation around the normal position. As a result, when therolling surfaces of the balls 17 come near the inner surface of thepockets 29, the balls 17 that are revolving quickly press against thefront inner surface of the pockets 29 in the direction of revolution,and similarly, the balls 17 that are revolving slowly press against therear inner surface. Therefore, large forces are applied to the tabsection 32 (see FIG. 2) that exists between a pair of adjacent pockets29 in the circumferential direction, such that the direction of theforce alternates in the circumferential direction, and thus durabilityof the retainer 27, which includes this tab section 32, is lost.

[0075] In contrast to this, if the inner dimension of the pockets 29 inthe circumferential direction of the retainer 27 is made 1.03 times ormore the diameter Da of the balls 17 as described above, it is possibleto prevent the balls 17 that are held in these pockets 29 from stronglypressing against the inner surface of these pockets 29. When the innerdimension is 1.03 times the diameter Da, there is a possibility that therolling surface of the balls 17 is pressed against the inner surface ofthe pockets 29, however, the amount is extremely small and can besufficiently absorbed through elastic deformation of the tab section 32with no problem. Furthermore, by making the inner dimension 1.035 timesor more the diameter Da, it is possible to sufficiently prevent therolling surfaces of the balls 17 from being pressed the inner surface ofthe pockets 29.

[0076] In order to increase the internal dimension of the pockets 29 inthe circumferential direction of the retainer 27, the entire innerdiameter of the pockets 29 can be increased, or it is possible to formthe pockets 29 in an oval shape that is longer in the circumferentialdirection.

[0077] In either case, the maximum value of the internal dimension inthe circumferential direction is, taking into consideration the overallstrength of the retainer 27, regulated by the relationship with thediameter Da. Normally, the maximum value of the inner dimension isregulated to be 1.1 times or less, or preferably, 1.05 times or less thediameter Da.

[0078] Also, this technique of improving the durability of the retainerby increasing the internal dimension of the pockets 29 in thecircumferential direction is not limited to the crown shaped retainershown in the figure, but can also be applied to machined cages orretainers having a rim section on both ends in the axial direction.Furthermore, the technique can of course be applied to this inventionwhich is directed to the rotation support apparatus for the compressorpulley as well as other uses for practicing the present invention.

[0079] As shown in FIG. 1, the radial ball bearing 14 constructed asdescribed above is installed between the inner peripheral surface of thefollower pulley 4 and the support cylinder 3 of the casing 2 to form therotation support apparatus for compressor pulley of this invention. Whenthe rotation support apparatus for compressor pulley is constructed inthis way, the center position (shown by the dot-dash line α in FIG. 1)in the width direction of the endless belt 11 that extends around theouter peripheral surface of the follower pulley 4, and the centerposition (shown by the dot-dash line β in FIG. 1), and the center of theball 17) in the width direction of the radial ball bearing 14 aredisplaced in the axial direction (left and right direction in FIG. 1) bythe amount δ (offset amount) shown in FIG. 1. In the case of therotation support apparatus for compressor pulley of this invention, theaforementioned offset amount δ is 40% or less of the diameter Dp of thepitch circle of the radial ball bearing 14 (see FIG. 2) (0.4 Dp≧δ).Preferably, this offset amount δ should be 20% or less (0.2 Dp≧δ), oreven more preferably 10% or less (0.1 Dp≧δ) of the diameter Dp of thepitch circle, in order to secure the durability of the radial ballbearing 14.

[0080] This point will be further explained with reference to FIG. 6,which shows the results of experiments performed by the inventors. FIG.6 is a graph showing the results of endurance tests that were performedin order to find out the effect that the ratio (δ/Dp) of the offsetamount δ of the acting position of the radial load from the center ofthe radial ball bearing 14 (center of each ball 17), with respect to thediameter Dp of the pitch circle of the balls 17 of the radial ballbearing 14 has on the life of the radial ball bearing 14. FIG. 6 showsthe ratio (δ/Dp) of the offset amount δ and the diameter Dp of the pitchcircle along the abscissa, and shows the life ratio (dimensionlessnumber) on the ordinate.

[0081] The life ratio that is shown on the ordinate shows that 1 is thelife necessary for practical use, and when this life ratio is 1 orgreater, then the construction can withstand practical use, however,when this life ratio is less than 1, then the construction cannotwithstand practical use. This life ratio is found under the followingconditions by operating the radial ball bearing 14 with the inner race16 fixed and rotating the outer race 15.

[0082] Rpm: 10,000 rpm

[0083] Temperature: Normal room temperature

[0084] Radial load: 2,254 N

[0085] The inventors changed the offset amount δ five times within therange 11.5% to 46% and measured the life (durability) at each for aplurality of specimens. The vertical lines along the dashed line ‘a’ inFIG. 6 that correspond to the five offset amounts δ show the range ofvariation in the test results for the plurality of specimens, and theblack dots on these vertical lines show the average values of thesespecimens.

[0086] As can be seen from the test results shown in FIG. 6, when theoffset value δ is kept at 40% or less of the diameter Dp of the pitchcircle of the radial ball bearing 14, it is possible to realize aconstruction which is capable of withstanding practical use securing thelife necessary for practical use.

[0087] However, in contrast to this, when the offset value δ exceeds 40%of the diameter Dp of the pitch circle of the radial ball bearing 14,the durability of the radial ball bearing 14 rapidly worsens. Moreover,when the offset value δ is kept to 20% or less of the diameter Dp of thepitch circle, it is possible to secure the life of the radial ballbearing 14 at 8 times or more the value necessary for practical use.Furthermore, when the offset value δ is kept at ¹⁰% or less of thepitch-circle diameter Dp, it is possible to secure the life of theradial ball bearing 14 at about 10 times the value necessary forpractical use.

[0088] When using this kind of rotation support for compressor pulley,moment loads that are proportional to the aforementioned offset amount δare applied to the radial ball bearing 14 by way of the follower pulley4 due to the tension of the endless belt 11. In addition, the centeraxis of the outer race 15 and the center axis of the inner race 16 ofthe radial ball bearing 14 have a tendency to become misaligned (totilt). However, in the case of this invention, even in this kind ofcase, it is possible to suppress any increase in resistance to rotationof the radial ball bearing 14, while at the same time, suppressmisalignment of the center axis of the outer race 15 and the center axisof the inner race 16 of the radial ball bearing 14.

[0089] In other words, the radial clearance for a standalone radial ballbearing 14 is kept at 0.2% or less of the pitch-circle diameter Dp ofthe radial ball bearing 14, or 1.5% or less of the diameter Da of theballs 17, so it is difficult for the aforementioned center axes tobecome misaligned. Also, the offset amount δ of the winding position ofthe endless belt 11 with respect to the radial ball bearing 14 is keptat 40% or less, or preferably 20% or less, and even more preferably 10%or less of the pitch-circle diameter Dp, so it is possible to keep themoment load applied to the outer race 15 by way of the follower pulley 4small.

[0090] This makes it possible to suppress tilting of the follower pulley4 and outer race 15 with respect to the inner race 16 and to preventexcessively large surface pressure from acting on the areas of rollingcontact in radial ball bearing 14, and makes it possible to secure thedurability of the radial ball bearing 14. Moreover, it makes it possibleto prevent eccentric wear of the endless belt 11 that extends around thefollower pulley 4 and to secure the durability of the endless belt 11.

[0091] In order to prevent misalignment of the aforementioned centeraxes and to remove the moment load caused by that misalignment, theoffset amount δ is made zero, or in other words, matching the centerposition α in the axial direction of the position where the endless belt11 is wound around the outer peripheral surface of the follower pulley4, with the center position β in the axial direction of the radial ballbearing 14 is considered to be possible.

[0092] However, by doing this, it becomes easy for wear and heat tooccur due to slipping at the contact points between the rolling surfaceof the balls 17 and the outer-ring raceway 18 and inner-ring raceway 19.That is, when the offset amount δ is made zero in order to remove themoment load, the surface pressure at the four contact points, two pointsof contact each between the rolling surface of the balls 17 and theouter-ring raceway 18 and inner-ring raceway 19, becomes nearly the sameon both sides in the axial direction. When the follower pulley 4 rotatesin this state, it becomes easy for large slippage to occur at thesepoints of contact, and thus it becomes easy for heat to be generated inthe radial ball bearing 14. In addition, as heat is generated, there isa possibility that the rolling fatigue life of the radial ball bearing14 will decrease.

[0093] In consideration of the above problems, with this invention it ispossible to make the minimum value of the offset amount δ 1 mm or more(δ≧1 mm). By making the minimum value of this offset amount δ 1 mm ormore, a pressure difference in surface pressure at the contact points onboth sides in the axial direction is formed, and this makes it possibleto prevent the occurrence of large slippage at the contact points andmakes it possible to lengthen the rolling fatigue life of the radialball bearing 14.

[0094] The explanation above, is made on an embodiment of a radial ballbearing 14 of the 4-point contact type in which the rolling surface ofthe balls 17 comes in contact with the outer-ring raceway 18 andinner-ring raceway 19 at two points each for a total of four points,however, as shown in FIG. 10, similar results can also be obtained for aradial ball bearing 14 of the 3-point contact type in which the rollingsurface of the balls 17 comes in contact with the inner-ring raceway 19at one point, and the outer-ring raceway 18 at 2 points.

[0095] The inventors found the relationship between the offset amountand the life ratio for this kind of radial ball bearing of the 3-pointcontact type as well. The test results of these experiments are shown inFIG. 6 together with the results for the 4-point contact radial ballbearing 14. The vertical lines along the dashed line ‘b’ in FIG. 6 thatcorrespond to the five offset amounts δ show the range of variation inthe test results for the plurality of specimens for a radial ballbearing 14 of the 3-point contact type, and the white dots on thesevertical lines show the average values of the specimens.

[0096] As can be seen from the test results shown in FIG. 6, in the caseof the radial ball bearing 14 of the 3-point contact as well, when theoffset amount δ is kept to 40% or less of the pitch-circle diameter Dpof the radial ball bearing, construction that secures the life necessaryfor practical use, and which is capable of withstanding practical use ispossible. However, in contrast to this, when the offset value δ exceeds40% of the diameter Dp of the pitch circle of the radial ball bearing14, the durability of the radial ball bearing 14 rapidly worsens.Moreover, when the offset value δ is kept to 20% or less of the diameterDp of the pitch circle, it is possible to secure the life of the radialball bearing 14 at 12 times or more the value necessary for practicaluse. Furthermore, when the offset value δ is kept at 10% or less of thepitch-circle diameter Dp, it is possible to secure the life of theradial ball bearing 14 at about 13 times the value necessary forpractical use. As can be clearly seen from FIG. 6, when comparing thelives of the radial ball bearings, the life of the 3-point contact typeradial ball bearing 14 is longer than the life of the 4-point contacttype radial ball bearing 14.

[0097] However, in regards to the inclination angle of the followerpulley when a moment load is applied to the follower pulley that issupported by the ball bearing 14, the inclination angle of the followerpulley that is supported by the 3-point contact type ball bearing 14 islarger than the inclination angle of the follower pulley that issupported by the 4-point contact type ball bearing 14. Also, the life ofthe endless belt that extends around the follower pulley that issupported by the 3-point contact type ball bearing 14 is shorter thanthe life of the endless belt that extends around the follower pulleythat is supported by the 4-point contact type ball bearing 14.Therefore, in an actual case, depending on the use, the balance betweenthe life of the radial ball bearing 14 and the life of the endless beltis taken into consideration in selecting whether to use the 3-pointcontact type or 4-point contact type for the radial ball bearing 14.

[0098] Furthermore, the invention described above was applied toconstruction having an electromagnetic clutch for engaging ordisengaging the pulley and rotating shaft, however, as long as theconstruction allows for rotation force to be freely transmitted from thepulley to the rotating shaft, the invention can also be applied toconstruction not having an electromagnetic clutch. In other words, inthe case of a swashplate-type variable displacement compressor asdisclosed in Japanese Patent Publication No. Tokukai Hei 11-210619 orJitsukai Sho 64-27482, by making the inclination angle of the swashplatesmall (or furthermore zero), it is possible to make the rotation torqueof the rotating shaft of the compressor very small.

[0099] In the case of this construction, as shown in FIG. 11, there isalso the case of connecting the follower pulley 4, which is rotatablysupported by the rolling bearing 30 around the support cylinder section3 that is formed on the end of the casing 2, to the rotating shaft 1 byway of a cushioning material 31 that functions as a torque tube, suchthat rotation force can be freely transmitted as long as no excessivetorque is applied, in which case there is no electromagnetic clutch.

[0100] With this construction, a single-row 3-point contact type or4-point contact type of the radial ball bearing, as shown in the figure,is used as the rolling bearing 30, and by regulating the relationshipbetween the position of the rolling bearing 30 and the follower pulley 4as shown in FIG. 1, it is possible to obtain the function and effect ofthis invention. This construction is also part of this invention. Whenthe present invention is applied to this kind of construction, thespecifications of the components of the rolling bearing 30 of the3-point contact type or 4-point contact type, and the positionalrelationship of the rolling bearing 30 and follower pulley 4 are thesame as shown in FIG. 1 and FIG. 2.

[0101] Also, in the case that at least one member of the inner races 16,outer races 15 and balls 17 (see FIGS. 1, 2 and 10) of the radial ballbearings 14 and rolling bearing 30, is made of steel, such as carbonsteel, bearing steel or stainless steel, then it is preferred that atleast one of these members 16, 15, 17, is treated by either nitriding ordimension stabilization, to secure the durability of the radial ballbearings 14 or rolling bearing 30.

[0102] In other words, when a single-row ball bearing such as the radialball bearing 14 or rolling bearing 30 is operated with an offset loadapplied, the surface pressure at the areas of contact between therolling surface of the balls 17 and the inner-ring raceway 19 andouter-ring raceway 18 becomes high. When elastic deformation becomeslarge due to this surface pressure, the rolling fatigue life of themembers and therefore the durability of the radial ball bearing 14 orrolling bearing 30 decreases, so by performing nitriding it is possibleto increase the surface hardness of the members, and thus it is possibleto suppress elastic deformation and prevent wear.

[0103] Moreover, during operation under offset loading, the amount ofheat generated increases, and thus it becomes easy for the dimensions ofthe components of the radial ball bearing 14 or rolling bearing 30 tochange, so by performing dimension stabilization, it is possible tosuppress changes in dimensions regardless of the generation of heat.

[0104] Of these, nitriding is a process of hardening the surface layerwith a solid solution of C and N, and the hardness of the surfaceincreases after treatment. By performing nitriding, there is a very hardnitride layer on the surfaces of the inner race 16, outer race 15 andballs 17. In regards to the inner race 16, and outer race 15, when thereis a nitride layer on the inner-ring raceway 19 or outer-ring raceway18, there is no need for nitriding of other areas. However, since it istroublesome to form a nitride layer on just the portion of theinner-ring raceway 19 or outer-ring raceway 18, so in an actual case, itis preferred to for a nitride layer over the entire surface of the innerrace 16 and outer race 15.

[0105] The elastic deformation due to the surface pressure does notoccur the same for the inner race 16, outer race 15 or balls 17, anddiffers depending on the shape and material. For example, when thematerial is the same, it is easy for elastic deformation of theouter-ring raceway 18 and inner-ring raceway 19 to occur, however,difficult for elastic deformation of the rolling surface of the balls 17to occur. Also, it is preferred that nitriding be performed for all ofthe members, however, depending on the material, dimensions or shape, itis possible to perform it for only part, such as the inner race 16 andouter race 15.

[0106] Moreover, the aforementioned dimension stabilization is a heattreatment for the purpose of reducing the amount of residual austenite γR, wherein for example, by gradually cooling the material used formanufacturing the inner race 16 and outer race 15, the residual amountof austenite γ R is reduced to 6% or less by volume. By performing thiskind of dimension stabilization it is possible to prevent the dimensionsand shape of the component materials from changing much from the normalvalue even when the temperature of the component materials of the radialball bearing 14 or rolling bearing 30 increases, as well as it ispossible to prevent the radial ball bearing 14 or rolling bearing 30from changing from the normal state, and thus it is possible to improvethe durability of the bearings 14, 30.

[0107] This nitriding or dimension stabilization can of course beperformed for the compressor pulley rotation support apparatus as wellas for other uses to which the present invention is applied.

[0108] Furthermore, it was not shown in the drawings, however, by makingthe width dimension of the cross section of the radial ball bearing 1.3times or more the height in the radial direction, it is possible toenlarge the volume of the internal space of the radial ball bearing andthus increase the amount of grease that can be filled into this internalspace. As a result, it is possible to lengthen the life of the greaseand improve the durability of the radial ball bearing. This technique ofincreasing the width dimension of the cross section can of course beperformed for the compressor pulley rotation support apparatus of thisinvention as well as for other uses to which the present invention isapplied.

[0109] The rotation support apparatus for compressor pulley of thisinvention, is constructed and functions as described above, and makes itpossible to secure the allowable moment load without increasing thedimensions in the axial direction, as well as makes it possible tosuppress heat and wear that occur during operation. Therefore, it ispossible to lengthen the life of the rolling bearing incorporated in therotation support apparatus for compressor pulley, and the life of theendless belt that extends around the pulley that is supported by therolling bearing, which contributes to making it possible to make variousmachinery, such as the compressor for air-conditioning equipment of anautomobile, more compact and higher quality.

What is claimed is:
 1. A rotation support apparatus for compressorpulley comprising a rotating shaft for a compressor; a stationarysupport section formed around the rotating shaft; a rolling bearingsupported by this stationary support section; and a pulley rotatablysupported by the rolling bearing around the support section, and aroundwhich an endless belt is extended, the rolling bearing being a radialball bearing of the single-row 3-point contact or 4-point contact typecomprising an inner race having an outer peripheral surface formed withan inner-ring raceway, an outer race having an inner peripheral surfaceformed with an outer-ring raceway, and a plurality of balls located andfreely rotating between the inner-ring raceway and outer-ring raceway,the outer peripheral surface of the inner race shaped such that it comesin contact with the rolling surface of the balls at one or two points,the inner peripheral surface of the outer race shaped such that it comesin contact with the rolling surface of the balls at one or two points,such that at least one of the inner-ring raceway and outer-ring racewaycomes in contact with the rolling surface of each of the balls at twopoints, the pulley having an outer peripheral portion that comes incontact with the endless belt, such that the distance in the axialdirection between the center of the endless belt coming in contact withthe outer peripheral surface portion of the pulley and the center of theradial ball bearing is 40% or less of the diameter of the pitch circleof the radial ball bearing.